3.4 Adobe Preservation-Fort Selden Adobe Test Wall Project
The Getty Conservation Institute
Museum of New Mexico
University of Queensland
Neville Agnew
Richard L. Coffman
Charles Selwitz
Michael Taylor
Kevin McDougall
Period of Activity: Current Research
Project Abstract
This project is concerned with developing techniques for the preservation of archaeological and historic adobe/mudbrick structures. The strategy is to test the effectiveness of the following methods and materials in preserving adobe from weathering by rain, snow, wind, and basal erosion by combined natural and accelerated outdoor weathering.
a.) chemical preservation including consolidation
b.) shelters and aerotextile fabrics shelters
c.) drainage
d.) nonwoven geotextile fabrics
e.) reinforcing geobars
Major Findings and Recommendations
Commercially available diisocyanate prepolymers and silanes that polymerize in situ by reaction with environmental moisture are being evaluated as adobe consolidantsin field trials of test walls, using a water-spray program and natural weathering. At low polymer loadings, in the range of 1-5%, the effectiveness of diisocyanates, such as the trimer of hexamethylene diisocyanate (Desmodur N3390, trimer of hexamethylene diisocyanate (manufactured by Mobay) is found to be a function of the amount of polymer put into the adobe. Bulk infiltration is more effective than surface brushing. This procedure provides almost perfect stabilization. Cracking, separation of plaster coat, and erosion does not occur. Brushing, when done with DN3390 in MEK-toluene, gives protection ranging from poor to good, depending upon the amount of polymer applied. Since bulk infiltration on large structures is impractical in terms of labor and materials, further work on additional test walls has concentrated on achieving deep penetration by using a larger number of coatings at higher dilution.
With silanes (Stone Strengthener H and Stone Strengthener OH supplied by ProSoCo) better results are obtained with H than with OH. When H is used, structural cracking of mud plaster and walls does not occur, however, the water spraying causes an erosional deterioration of the surface that is not found with isocyanate-treated walls. The quality of the stabilization is not dependent on the amount of H applied, and this probably results from the larger quantities used, i.e., approximately twice as much as DN3390, as recommended by the supplier. Comparatively poor results, with one wall treated with Acryloid A-21, ProSoCo) better results are obtained with H than with OH. When H is used, structural cracking of mud plaster and walls does not occur, however, the water spraying causes an erosional deterioration of the surface that is not found with isocyanate-trea;suggest that acrylic polymers will not be as effective as isocyanates and silanes.
Tests are being carried out on the physical protection provided against weathering by knitted shadecloths (aerotextiles). With these materials interposed between the spray nozzle and the test wall, greatly reduced erosion is found through breaking the force of the water-spray. It was found that a water-sprayed wall draped with a geotextile, Mirafi-140N, maintained its integrity while an uncovered control wall quickly disintegrated. This demonstrates a useful procedure for the reburial of an archaeological adobe site.
Other preservation techniques such as drains and reinforcing geobars are not at present sufficiently advanced in testing for results to be reported.
Primary Publications
Agnew, N., "Adobe Preservation," Report on a three-month research project at the Getty Conservation Institute, March 1987.
ABSTRACT-This report is in three parts: (1) An outline of the composition, physicochemical behavior, and mechanical properties of the composite material adobe. A brief review of some of the more important work in the areas of adobe weathering and preservation research and technology. Suggested research lines that have come out of the Getty Conservation Institute study. (2) The results of the laboratory testing and evaluation of a range of chemical preservatives for adobe. (3) Directions for future research with New Mexico State Monuments into chemical preservation, site shelter designs and materials, ground water control, and backfilling and reinforcing techniques, using Fort Selden, New Mexico, as a field-testing facility.
Agnew, N., J. R. Druzik, T. Caperton, and M. Taylor, "Adobe: The Earliest Composite Material," Working Group 10, ICOM Committee for Conservation, Preprints, Vol. 2, Sydney, Australia, 1987, pp. 439-446.
ABSTRACT-Work in progress from two concurrent programs of research on adobe is outlined. A five-year field experiment is under joint supervision with New Mexico State Monuments (NMSM) to derive results for future restoration projects and to provide baseline data for new construction. Laboratory work at the Getty Conservation Institute (GCI) is investigating high performance polymer systems applied to adobe.
Agnew, N., F. Preusser, and J. R. Druzik, "Strategies for Adobe Preservation-The Getty Conservation Institute Research Program," ICCROM, 5th International Meeting of Experts on the Conservation of Mudbrick, Rome, November 1987.
ABSTRACT-Laboratory research at the Getty Conservation Institute and the Queensland Museum has shown the potential of a number of techniques and materials for the preservation of archaeological and historic adobe.These are: polyisocyanates and silanes as chemical preservatives, permeable aerotextiles for site shelters, geotextiles for drainage, and the use of composite synthetic fiber geobars as structural reinforcing elements. The next phase in the strategy of the program is field testing of the laboratory results in conjunction with the existing trials being conducted by the New Mexico State Monuments on test walls at Fort Selden. The experiments are due to start at the beginning of 1988 on thirty test walls. Research design for field testing is presented. Results will be applied to a real site for further evaluation prior to eventual dissemination of the findings in the GCI technical report series Research in Conservation.
Druzik, J. R., N. Agnew, T. Caperton, and M. Taylor, "Recent Activity in Adobe Preservation Research," WAAC Annual Meeting, Tucson, Arizona, November 1987.
ABSTRACT-Three institutions are currently united in a collaborative research program on adobe preservation. New Mexico State Monuments (NMSM), the Queensland Museum in Australia, and the Getty Conservation Institute have been investigating a multidisciplined approach that includes: chemical consolidation, control of rain and wind erosion, structural reinforcement, documentation, and predicted weathering through the use of computer modeling and photogrammetric imaging.
Coffman, R. L., "Status of Research on the Consolidation of Earthen Materials," WAAC Annual Meeting, Honolulu, Hawaii, October 1989.
ABSTRACT-Field and laboratory studies are being conducted to evaluate the performance of isocyanates as a treatment for earthen materials. Various application techniques, solvent systems, and solution concentrations have been tested to determine the most effective method for consolidating and improving the physical properties of adobe, sand, clay mixtures, and clay-bearing materials. Preliminary evaluations indicate that enhanced consolidation, compressive strength, and water repellency result from the treatment of the above materials with isocyanates. Additional research on depth of penetration, effects of weathering, and discoloration are in progress. The possibility of treating historic earthen materials is promising but additional research is necessary before widespread usage of isocyanates could be considered.
Taylor, M., and N. Agnew, "Adobe Conservation: Research and Applications," APT89 Chicago Conference, Make No Little Plans, Chicago, Illinois, September 4-9, 1989.
ABSTRACT-None available.
Agnew, N., "The Getty Adobe Research Project at Fort Selden. I. Experimental Design for a Test Wall Project," Adobe 90, Preprints of the 6th International Conference on the Conservation of Earthen Architecture, Las Cruces, New Mexico, October 14-19, 1990, pp. 243-249.
ABSTRACT-The Getty Conservation Institute, in association with the Museum of New Mexico State Monuments, began a field-test program early in 1988 at Fort Selden State Monument in southern New Mexico. The purpose is to evaluate, using adobe test walls, various preservation materials and techniques. These include chemical consolidants (mainly diisocyanates and silanes); techniques of application of consolidants (spraying, brushing, bulk infiltration); surface and depth treatments; drainage, shelter design, and materials; reburial techniques for archaeological sites; and some structural reinforcing materials and methods. Accelerated aging through water spray has been used on the walls and their condition has been monitored stereophotographically. This paper presents the experimental design. Some preliminary results are given in subsequent papers in the present preprints.
Selwitz, C., Coffman, R., and N. Agnew, "The Getty Adobe Research Project at Fort Selden. III. An Evaluation of the Application of Chemical Consolidants to Test Walls," Adobe 90, Preprints of the 6th International Conference on the Conservation of Earthen Architecture, Las Cruces, New Mexico, October 14-19, 1990, pp. 255-260.
ABSTRACT-Silane esters and polyisocyanates were applied to adobe test walls in various concentrations and solvent mixtures by spraying, brushing, multiple coating, and bulk infiltration. After one month's curing they were subjected to an accelerated weathering regime of two water spray cycles per day for two months, and subsequently they were allowed to weather naturally. The walls were evaluated visually according to a numerical rating system. Isocyanates provide very effective stabilization by a combination of brushing and bulk infiltration, but there must be a suitable network of accession holes for deep delivery of polymer, and the amount of consolidant must be optimized. The silane ester formulation, Stone Strengthener H, is easier to apply and gives good consolidation without discoloration; but the treated walls show erosion not seen with isocyanate-treated walls. Old aged adobe may require a rehydration before either consolidation can be done.
Agnew, N., and R. Coffman, "Thermal Monitoring Thermal Monitoring of Adobe Test Walls at Fort Selden," Adobe 90, Poster presented at the 6th International Conference on the Conservation of Earthen Architecture, Las Cruces, New Mexico, October 14-19, 1990.
ABSTRACT-Temperature-sensing thermocouples (T-type, copper-constantan) were implanted into the north and south faces, on plastered and unplastered sides, of several adobe test walls at Ft. Selden, New Mexico. The thermocouples were embedded as pairs with one located just below the surface (~2.5 cm) and the other halfway into the wall (~12 cm). The thermocouple pairs were located near the top, middle, and bottom of full-size walls (1.5 m x 1.5 m x 0.25 m), and near the top and bottom of half-size walls (0.75 m x 1.5 m x 0.25 m). This distribution of thermocouples permits lateral and vertical thermal variations within the test walls to be recorded. The temperatures were recorded using 4-, 8-, or 16-channel data loggers and collected over 24-hour time intervals, when possible. Seasonal, daily, and hourly temperature variations were obtained and compared. The results show that temperature gradients as large as 30 °C can develop which could affect the physical state of the wall.
Agnew, N., and R. Coffman, "The Hexashelter-A New Shelter Structure for Archaeological Sites," Adobe 90, Poster presented at the 6th International Conference on the Conservation of Earthen Architecture, Las Cruces, New Mexico, October 14-19, 1990.
ABSTRACT-A new style of protective shelter protective shelter ;was designed by one of the authors (NA) and built by the Getty Conservation Institute to address problems commonly faced at archaeological sites. This shelter was designed to be lightweight, modular, easy-to-erect, inexpensive, and temporary. It has a zigzag profile and six sides, hence the name "hexashelter" for the hexagonal shape of each module. It is made of aluminum tubing and fabric, and being modular it can be added on to laterally without difficulty by building out from any of the six sides. It can be built in a relatively short period of time with a small work crew and does not require heavy construction equipment. Its footings sit completely above ground eliminating need for below surface excavation, an important consideration in an archaeological site. It is inexpensive and relative to a conventional permanent house-type of shelter building, and can be easily dismantled leaving little evidence of its prior presence. The Fort Selden hexashelter, which covers 160 square meters (1700 square feet), is the second of its kind to be erected. A version was built over mosaics in Paphos, Cyprus, Paphos, Cyprus,; in 1989. The photographs on the poster show the stepwise manner in which the hexashelter hexashelter; was constructed at Fort Selden.
Selwitz, C., "Saving the Fort Selden Ruins: The Use of a Composite Blend of Chemicals to Stabilize Fragile Historic Adobe," Conservation and Management of Archaeological Sites, James & James Publishers, Vol 1, 1995, pp. 109-116.
ABSTRACT- A four-step process for the stabilization of fragile, exposed historic adobe structures has been developed. The structures are first stabilized by consolidation with an alkoxysilane. Protection for the tops of walls in provided by capping with mud made with an acrylic polymer emulsion instead of water. A similar modified mud is then sprayed over the entire structure to provide a veneer that does not significantly change the appearance of the wall surface. Finally, when dry, this is covered with a polysiloxane water repellent. Small test sections of the walls of the abode ruins at Fort Selden, New Mexico, USA, were subjected to various treatment combinations. After two winters, it was found that the four-step procedure gave the best results.
Secondary Publications
Druzik, J. R., and D. R. Stuart, "The Collections Environment and Management." In Conservation in Historic Adobe Museums: A Primer, eds. David R. Stuart and Paul Leitzell, City of San Buenaventura, Department of Parks and Recreation, June 1986, pp. 30-41.
ABSTRACT-Factors contributing to the indoor microenvironment within historical adobe structures include temperature temperature ;and relative humidity relative humidity;, air pollution, dust, light, insects, and handling.
Druzik, J. R., and D. R. Stuart, "Condition Documentation and Housekeeping." In Conservation in Historic Adobe Museums: A Primer, eds. David R. Stuart and Paul Leitzell, City of San Buenaventura, Department of Parks and Recreation, June 1986, pp. 43-51.
ABSTRACT-Condition documentation and housekeeping of collections housed and displayed within adobe historical structures are addressed in this chapter.
Weintraub, S., J. R. Druzik, and B. Johnson, "Conservation in Historic Adobe Structures," Seminar/Workshop, Olivas Adobe Historical Park, Ventura, California, October 24-25, 1986.
ABSTRACT-The preventive conservation of small collections in historical adobe structures is based to a large extent on common sense and the selective application of methodologies originally established in large museums. This aspect of the seminar/workshop was explored for caretakers of these collections who are outside the normal stream of museology.
McDougall, K., N. Agnew, and M. Taylor, "The Use of Photogrammetry to Determine Erosion Rates of Adobe," Adobe 90, Poster presented at the 6th International Conference on the Conservation of Earthen Architecture, Las Cruces, New Mexico, October 14-19, 1990.
ABSTRACT-A combination of historical and recent photography has been used to determine some approximate erosion rates of adobe at Fort Selden. The feasibility study funded by the Getty Conservation Institute examined a number of different analyses and measurement processes to determine average erosion rates. A simple computer measurement and modeling process permitted data to be extracted quickly and accurately from the photography using the technique of photogrammetry.